Organic based solar cells have distinct advantages over their inorganic counterparts, such as low cost of fabrication, ease for large area processing, and compatibility with flexible and light weight plastic substrates, and thus have attracted enormous amount of research interest and effort in the past decades. However, the organic cells typically suffer from the low efficiency of light conversion (usually less than 5%) that inhibits their use in practical applications at the present.
The efficiency of organic solar cells is largely determined by four basic, consequential processes: exciton diffusion; charge generation via electron transfer; charge separation and transport. Although recent developments of bulk-heterojunction materials (e.g., polymer/C60) has shown promise in improving the first two processes by creating charge separation via photoinduced intra- and inter-molecular electron transfer, the poor organization and/or phase segregation of the bulk-mixed materials still limit the charge transport.